1. Field of the Invention
The present invention relates to a liquid discharging head for effecting printing by discharging printing (recording) liquid from a discharge port by means of thermal energy, and a liquid discharging apparatus utilizing such head. The above-mentioned printing includes ink application onto various kinds of ink substrate capable of receiving ink, such as cloth, fiber, paper and sheet material, and the above-mentioned apparatus includes all the information processing apparatus and printers serving as the output apparatus for such information processing apparatus, and the present invention is applicable to such printing or apparatus.
2. Related Background Art
Ink jet printing method is recently attracting attention because of its features that the noise at the printing operation can be reduced to a negligible level, that high-speed printing operation is possible and that image fixation on so-called plain paper is possible without particular treatment.
Among such ink jet printing technologies, the ink jet printing method disclosed for example in the Japanese Patent Laid-Open Application No. 54-51837 and the German Patent Laid-Open Application (DOLS) 2843064 is different from other ink jet printing methods, in that the driving force for ink discharge is obtained by applying thermal energy to liquid.
More specifically, in the ink jet printing method disclosed in the above-mentioned patent applications, the liquid effected by thermal energy undergoes a state change involving a rapid volume change, and is discharged from an orifice at the front end of a printing head, by the force generated by such state change. The discharged liquid forms a flying droplet, which is deposited onto a printing material to perform recording.
In particular, the ink jet printing method disclosed in the above-mentioned DOLS 2843064 is not only extremely advantageously applicable to so-called drop-on-demand printing method, but also has the advantage of providing a high-quality image of a high resolving power at a high speed, since a full-line head with multiple orifices arranged at a high density can be easily realized.
The printing head employed in the above-mentioned ink jet printing methods is composed, as shown in FIG. 1, of an ink discharge unit including orifices (discharge ports) 206 for discharging liquid droplets, plural nozzles 204 communicating with the orifices 206, provided in a part thereof with heat action portions where the thermal energy for liquid discharge is applied to the liquid and divided by flow path walls 203, and a common liquid chamber for supplying the nozzles 204 with recording liquid, electrothermal converting members (heat generating members) 202 serving as means for generating thermal energy, and a printing head substrate 201 provided with a wiring portion 209 for supplying the heat generating members 202 with electric currents. The liquid is supplied to the common liquid chamber 207 from an unrepresented liquid reservoir tank through a supply pipe 208.
In such conventional ink jet printing technologies, the ink jet recording head utilizing pigment ink has been associated with the drawbacks that the ink is of a limited pot life as it tends to solidify by the coagulation of the pigment component, that the response frequency of ink discharge cannot be made high because of the high viscosity of ink, and that the time required for image fixation is extremely long because of poor permeability of such ink into the recording paper. It has been tried to overcome such drawbacks by reducing the pigment concentration or by employing a solvent of higher permeability, but such measures result in a loss in the recording density or blotting of the ink on the recording paper and are not effective sufficiently.
On the other hand, the Japanese Patent Laid-Open Application proposes an ink jet recording method of superposing the recording ink and a process liquid for improving the image quality, storage durability and liquid permeability. In this proposed method, the color ink jet recording apparatus is provided with separate drum-structured heads.
In such recording method, however, the image quality, image fixation and image durability become significantly deteriorated if the hit position of the processing liquid is displaced even slightly from that of the recording ink. In particular, in the above-mentioned conventional configuration in which the head for the processing liquid and that for the recording ink are formed separately, the components of the recording heads and of the printer main body, particularly the carriage unit thereof, have to be highly precisely prepared in order to match the his positions of the processing liquid and the recording ink, thus leading to a higher cost. Also these parts require an enormously long time for the adjustment, and, for these reasons, such ink jet printer is much more expensive in cost than the ordinary ink jet printers. These drawbacks are particularly conspicuous in the printer in which the user can replace the recording heads. Also it will be easily understood that the printing speed cannot be much improved even if the response speed is increased. These drawbacks are similarly encountered also in the recording method in which inks of different kinds are to be deposited on a same hit position.